Comparative efficacy of a novel intramammary dry cow antibiotic to eliminate subclinical mastitis in the dry period

Abstract

Although there is increasing concern over routine administration of long-acting antibiotics to all cows at the end of lactation, the practice is required to eliminate subclinical infections that are present at drying off. Alternatives to dry cow therapy (DCT) for preventing new infections from occurring in uninfected quarters in the dry period are increasingly common. However, until a cost-effective and reliable test becomes available to determine which cows and quarters are not infected at drying off, administering DCT to all quarters and all cows remains the recommended practice. The efficacy of a novel intramammary treatment containing tilmicosin, administered at drying off to eliminate mastitis pathogens other than Staphylococcus aureus, was compared to intramammary cloxacillin. Data from 406 infected quarters, representing 238 cows that either received intramammary tilmicosin or benzathine cloxacillin, were analysed. The study was conducted in Ontario, Quebec, and Prince Edward Island in Canada for a period of one year, beginning in July 1999. Results showed that 11% of quarters had a major mastitis pathogen recovered prior to the dry period. The overall cure rate of mastitis pathogens following administration of DCT was 89.2%. The cure achieved with intramammary tilmicosin was 87.2%, whereas for cloxacillin it was 90.9%. There was no significant difference in the cure rate between the 2 treatments, either in overall cure, or cure of any specific pathogen. Results of the final logistic regression models to determine factors associated with the probability of infected quarters to cure during the dry period reemphasized the importance of dry period length, season of drying off, and general environmental exposure. It is concluded that intramammary tilmicosin is as efficacious as benzathine cloxacillin for eliminating existing infections caused by pathogens other than S. aureus during the dry period. No commercial preparation of intramammary tilmicosin is currently available.